I need to send my computer in to be repaired and I need to back up my data, where do I start?
Before thinking about how to backup, first you need to decide what to backup. The choice is always yours, but I would recommend anything that you would require later on and would not be able to recreate, so important electronic documents, (tax things, business things, anything scanned and original disposed of) photos, memorabilia, videos. If you have bought films or music or other media on-line, you may still be able to download it from the original source.
You could then back up your data with an external hard drive, and also use the Windows built-in app (the File Recovery tool in Windows 7, or the File History tool in Windows 8) to create a system image and a recovery CD/flash drive. Subsequently, use Windows Backup to back up your important data daily, weekly, or monthly to the hard drive. Here is a link to the Windows repair and recovery page.
Another option is to use sites like Drop-box, Google drive or One drive to store your documents, files and photos. You can get limited free accounts, or if more storage if required they offer subscriptions for additional space.
I would always have a back up of important files. You never know when you might need it, and imagine how you would feel if you lost those important photos. Those memories are too precious not to be saved somewhere.